This invention relates to copying apparatus, and more particularly it is concerned with a copying apparatus of the type capable of copying and printing an image of a document on a printing sheet either on one or either side thereof.
Several types of copying apparatus have hitherto been available for copying and printing an image of a document on a printing sheet on either side thereof. Of these copying apparatus, the most common one is the type of copying apparatus shown in Japanese Patent Publication No. Sho-49-36264 in which a single photosensitive drum is used and the path of movement of printing sheets forms a loop including trays for supporting printing sheets to be printed on either side thereof. This type of copying apparatus has suffered the disadvantages that it has a high incidence of jamming of the printing sheets and a great deal of trouble occurs and that producing a copy printed with an image of a document on either side thereof is a time-consuming operation.
To obviate these disadvantages, improved copying apparatus capable of printing an image of a document on either side thereof have been developed, as described in U.S. Pat. No. 3,536,398 and Japanese Patent Application Laid-Open No. Sho-56-161559, which use two photosensitive drums for printing an image of a document on either side of a printing sheet. Some disadvantages are associated with this type of copying apparatus, too. For example, in this type of copying apparatus, it is necessary to bring images of a document printed on opposite sides of a printing sheet into alignment with each other and an optical system becomes complex in construction to attain the end.
Even if the copying apparatus used is for copying and printing an image of a document on either side of a printing sheet, the need often arises to produce a copy having an image of a document printed only on one side thereof. Copying apparatus of the prior art capable of copying and printing an image of a document on either side of a printing sheet are capable, of course, of printing an image of a document only on one side of a printing sheet. However, since a printing sheet is conveyed along the same path of travel when only one side thereof is to support an image of a document and when either side thereof is to support it, they suffer the disadvantage that producing copy having an image of a document only on one side thereof is a time-consuming operation. Moreover, even if these copying apparatus each have two photosensitive drums, they only have the function of copying apparatus having one photosensitive drum, so that their performance is not satisfactory.